The staging branch diverged from main before PR #542 landed and was never
forward-ported. a2a_tools.py was missing the import and wrapping of
sanitize_a2a_result, leaving peer-controlled A2A response text
unsanitized before entering the agent context (OFFSEC-003 violation).
Fix mirrors the main-line fix (PR #542 / mc#537):
- Import sanitize_a2a_result from _sanitize_a2a
- Wrap all peer-controlled return values with sanitize_a2a_result()
Also removes a duplicate dead-code block that was an artifact of the
merge conflict on the staging branch.
Fixes: molecule-ai/molecule-core#787
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>